D,L-2-amino-4-methylphosphinobutyric acid (hereinafter referred to as D,L-MPGA) and a salt thereof with an inorganic or organic base are useful not only as bactericides for agricultural and horticultural purposes (Japanese Patent Prepublications Nos. 14644/74, 14641/74 and 26430/74), but also as herbicides, particularly those for perennial weeds and miscellaneous shrubs (Japanese Patent Prepublication No. 139727/77).
A recent study on the herbicidal activity of the compounds has shown that the activity of L-MPGA is about twice as high as that of the racemic, i.e. D,L-MPGA, thus clarifying that the herbicidal nature of the compounds is essentially attributable to L-MPGA and not to D-MPGA.
It has already been proposed to prepare L-MPGA from a known antimicrobial agent, SF-1293 substance, that is L-MPGA-alanyl-alanine by an acid decomposition (Japanese Patent Prepublication No. 85538/73) or by an enzymatic decomposition (Japanese Patent Prepublication No. 31890/74). With respect to SF-1293 substance and its preparation, reference is made to Japanese Patent Prepublication No. 22688/73 and Helvetica Chimica Acta, 55, Fase 1, 224-239 (1972). On the other hand, chemical synthetic processes gave MPGA in the form of a racemic, D,L-mixture (Japanese Patent Prepublications Nos. 91019/73 and 139727/77).
We have studied on optical resolution of D,L-MPGA obtained by a chemical synthetic process and now found that N-acyl-D,L-MPGA can be optically resolved by a specific deacylation of N-acyl-L-MPGA with some acylases of microbial origin, so that L-MPGA can be isolated from N-acyl-D-MPGA.